Different implantable medical devices have been developed for treating a number of ailments associated with body lumens. In particular, occlusive devices are useful in filling vascular or other body spaces. Some body spaces, such as vascular aneurysms, are formed due to a weakening in the wall of an artery. Often these aneurysms are the site of internal bleeding and stroke. A variety of different embolic agents are known to be, at least arguably, suitable for treatment of these anomalies. These treatments are commonly known as “artificial vaso-occlusion.”
Over the past few years, advancements in the artificial occlusion of vessels and aneurysms have included the delivery and implantation of metal coils as vaso-occlusive devices. Implantable metal coils that are useful as artificial occlusion devices in vasculature lumens or aneurysms are herein referred to as “vaso-occlusive coils.” Vaso-occlusive coils are generally constructed of a wire, usually made of a metal or metal alloy that is wound to a helix. The vaso-occlusive coil assumes an irregular shape upon discharge of the device from the distal end of the catheter. A variety of vaso-occlusive coils are known. For instance, U.S. Pat. No. 4,994,069, issued to Ritchart et al., shows a flexible, preferably coiled, wire for use in small vessel vaso-occlusion. Unlike vaso-occlusive coils used prior to that time, Ritchart et al. teach a coil that is fairly soft and is delivered to the site using a pusher within a catheter lumen. Upon discharge from the delivery catheter, the coil may undertake any number of random or regular configurations used to fill the site.
The coils may be used for small vessel sites, e.g., 0.5-6 mm in diameter. The coils themselves are described as being between 0.010 and 0.030 inches in diameter. The length of the coil wire is typically 15 to 20 times the diameter of the vessel to be occluded. The wire used to make up the coils may be, for instance, 0.002 to 0.006 inches in diameter. Tungsten, platinum, and gold threads or wires are said to be preferred. These coils have a variety of benefits including the fact that they are relatively permanent, they may be easily imaged radiographically, they may be located at a well defined vessel site, and they can be retrieved.
In addition to the various types of space filling mechanisms and geometries of vaso-occlusive coils, other particularized features of coil designs, such as mechanisms for delivering vaso-occlusive coils through delivery catheters and implanting them in a desired occlusion site, have also been described. The examples of categories of vaso-occlusive coils based upon their delivery mechanisms include pushable coils, mechanically detachable coils, and electrolytically detachable coils.
One example of the type of vaso-occlusive coil referred to above as the “pushable coil” is disclosed in Ritchart et al., discussed above. Pushable coils are commonly provided in a cartridge and are pushed or “plunged” from the cartridge into a delivery catheter lumen. A pusher advances the pushable coil through and out of the delivery catheter lumen and into the site for occlusion.
Mechanically detachable vaso-occlusive coils are typically integrated with a pusher rod and are mechanically detached from the distal end of that pusher after exiting a delivery catheter. Examples of such mechanically detachable vaso-occlusive coils are found in U.S. Pat. No. 5,261,916 to Engelson or U.S. Pat. No. 5,250,071 to Palermo.
Finally, examples of electrolytically detachable vaso-occlusive coils may be found in U.S. Pat. Nos. 5,122,136 and 5,354,295, each issued to Guglielmi et al. In these devices, the vaso-occlusive portion of the assembly is attached to a pusher via a small, electrolytically severable joint. The electrolytically severable joint is severed by the placement of an appropriate voltage on the core wire. The joint erodes in preference either to the vaso-occlusive coil itself or to the pusher core wire.
As noted above, aneurysms present a particularly acute medical risk due to the dangers of potential rupture of the thin wall inherent in such aneurysms. Occlusion of aneurysms by use of vaso-occlusive coils without occluding the adjacent artery is a special challenge and is a desirable method of reducing such risk of rupture. These vaso-occlusive devices are typically placed in an aneurysm in a manner described in U.S. Pat. No. 4,739,768 issued to Engelson. In particular, a microcatheter is initially steered into or adjacent to the entrance of an aneurysm, typically aided by the use of a steerable guidewire. The wire is then withdrawn from the microcatheter lumen and replaced by the vaso-occlusive coil. The vaso-occlusive coil is advanced through and out of the microcatheter, desirably being completely delivered into the aneurysm.
However, after, or perhaps during, delivery of the coil into the aneurysm, there is a specific risk that a portion of the coil might migrate out of the aneurysm entrance zone and into the feeding vessel. The presence of the coil in that feeding vessel may cause a highly undesirable occlusion there. Also, there is a quantifiable risk that the blood flow in the vessel and aneurysm may induce movement of the coil farther out of the aneurysm, resulting in a more developed embolus in the feeding vessel.
One type of aneurysm, commonly known as a “wide neck aneurysm,” is known to present particular difficulty in the placement and retention of vaso-occlusive coils, because vaso-occlusive coils lacking substantial secondary shape strength may be difficult to maintain in position within an aneurysm no matter how skillfully they are placed. Wide neck aneurysms are herein referred to as aneurysms of vessel walls having a neck or “entrance zone” from the adjacent vessel, wherein the entrance zone has a diameter that either: (1) is at least 80% of the largest diameter of the aneurysm; or (2) is clinically observed to be too wide effectively to retain vaso-occlusive coils that are deployed using the techniques discussed above.
One approach to occlude such an aneurysm is described in U.S. Pat. No. 6,168,622, which describes a vaso-occlusive device with a secondary shape having a bulbous body portion and an anchor. The bulbous body portion is deployed within the aneurysm while the anchor is set just outside of the aneurysm, covering the aneurysm's neck or entrance zone. The device is integrally formed from a tube—clamped at both ends—of braided Nickel-Titanium (NiTi) wires. The bulbous body functions to occlude the aneurysm, while the anchor covers the entrance zone. In some cases, it may still be desirable to deploy vaso-occlusive coils with such a device, but the bulbous body of the vaso-occlusive device does not provide much space within the aneurysm to allow for insertion and deployment of the coils.
Accordingly, an improved system and method for occluding an aneurysm neck would be desirable.